Detonator and process of making



Patented Dec. 2, 1930 UNITED STATES PATENT OFFICE CLIFFORD A. WOODBURY, F MEDIA, PENNSYLVANIA, ASSIGNOR TO E. I. DU PONT DE NEMOURS & COMPANY, OF WILMINGTON, DELAWARE, A CORPORATION OF DELA- WARE DETONATOR AND PROCESS OF MAKING No Drawing.

My invention relates to an improved process for the manufacture of detonators. In particular it relates to the process of filling detonators by casting.

The usual practice in manufacturing blasting caps is to press into a metal shell a main or base charge at a pressure of approximately 300 kilograms per square centimeter and then follow this with a priming charge subjected 1 to a pressure of about 250 kg. per sq. cm. The explosives ordinarily used in base charges are trinitrotoluene, tetryl and picric acid. The most commonly used primers are mercury fulminate and lead azide.

From the viewpoint of the explosive strength of the detonator, it is desirable that the base charge have as great a density as practical. The density may be increased by using higher charging pressures. WVith ordi- 2o nary equipment, however, pressures above 300 kg. per sq. cm. cannot be used as this is the limit that the shell wall will stand.

British Patent No. 172,91t granted to Eschbach in 1921 discloses a method of making high density base charges by using a specially designed press in which the shell is placed in a die and pressed at high pressures (1000 kg. per sq. cm.) from both ends of the shell. This process, however, requires expensive equipment and greatly increases the hazard of the pressing operation.

\Vhile explosives have been cast for certain purposes, such as, for instance, loading military shell with trinitrotoluene, the process of casting so far as I am aware has never been applied to secondary detonating compounds or used in the manufacture of detonators. The explosive compositions commonly used in detonators do not lend themselves readily to casting, either because they cannot be melted with safety or because when cast they are too insensitive.

The usual method for casting explosive substances is to first melt the explosive in a 1 suitable heated receptacle and then to pour the molten explosive into the containers to be filled. With relatively safe explosives, such as TNT, and also in loading relatively large shells, this method is entirely satisfactory.

With such sensitive explosives as are used in Application filed May 3, 1928.- Serial No. 274,964.

detonators, this method of casting is not only unsafe but is also impractical because of the very small quantities of explosive used per detonator and the difficulty encountered in delivering an exact and uniform weight of explosive to each shell.

I have discovered that the desirable high density of the explosive in a detonator can be obtained by a process of casting. I have further discovered a satisfactory method of accomplishing this result by passing the shells loaded With loose granular explosive through a Warm chamber or bath and then cooling to obtain a cast charge.

Several advantages are gained by using this process. A charge of high density and great explosive strength is obtained. Expensive and hazardous high pressure machinery is eliminated. The process of casting lends itself more readily to quantity production than the method of using a pin press. It is simple, inexpensive and entirely practical.

It is the object of my invention to accomplish these advantages. Other objects and advantages will appear as the description proceeds.

I may use for my explosive to be cast any one of the many low melting compounds available. about 80 (1., trinitroanisol, melting at 68 (1, picric acid, melting at 122 G., trinitrobenzene, melting at 121 (1, etc. I prefer to use, however, an explosive melting at below 100 (3., and having a relatively high sensitiveness. Erythritol tetranitrate answers these requirements very satisfactorily as it melts at 61 C. and due to its very high degree of nitration is very sensitive. The preparation and properties of this explosive are described in co-pending application of F. H. Berzgeim, Serial No. 184,180, filed April 15, 192

My process of producing cast charges in a detonator tube or shell consists in charging the tube or shell with the low melting explosive in the granular form, subjecting the tube to suflicient heat to meltthe explosive and then solidifying the explosive by cooling. It is not necessary that the explosive consist of one single low melting compound. It

For example, TNT, melting at may consist of a mixture of two or more compounds, of such a nature that both melt down together when heated or only one melts down and settles around the grains of the other which remains in the granular form.

For example, I may charge grains of erythritol tetranitrate into the detonator tubes, using the usual form of charging blocks, pass the tubes through a heated chamber or bath and then through a cold chamber or bath, or I may charge a granular mixture of erythritol tetranitrate and tetryl (trinitrophenyl methyl nitramine) and then subject the tubes to a. temperature suilicient to melt the erythritol tetranitrate and then solidify by cooling. After loading the base charge in the above manner a. charge of initiating explosive such as fulminate or lead azide is pressed on top of the cast base load.

It is obvious that my process lends itself very readily to the production of cast charges composed of two or more explosives and that in this way cast charges which normally would be too insentitive for practical use in a detonator can be rendered sensitive by simply adding a sensitizing explosive. For example, cast charge comprised of a mixture of T NT and fulminate of mercury can very readily be produced by my process, the fulminate acting as a sensitizer of the cast TNT.

It is understood that, whereas I have described the application of my invention to the loading 01' detonator tubes or shells, I do not intend to limit myself solely to this use. My process of casting may be employed to advantage in the manufacture of booster charges for detonating military high explosives or wherever a charge of secondary detonating explosive is used.

I claim:

1. A process of loading detonator tubes which comprises charging the tubes with a mixture of at least two explosives, at least one of which melts at a temperature below 100 0., subjecting the charge to sufficient heat to melt the low melting constituent, and then solidifying the charge by cooling.

2. A process of loading detonator tubes which comprises charging the tubes with erythritol tetranitrate in admixture with at least one other solid explosive, subjecting the tubes to sutlicient heat to melt the erythritol tet-ranitrate and then solidifying the charge by cooling.

3. A process of loading detonators which comprises casting in the detonator shell a mixture of at least two explosives, at least one of which acts as a sensitizing agent.

4. A booster charge for detonating high explosives comprising a cast charge of a mix ture of at least two explosives, at least one of which melts at a temperature below 100 C.

5. A booster charge for detonating high explosives comprising erythritol tetranitrate CLIFFORD A. IVOODBURY. 

